Off the Leash is a game that arrived a little while ago on the iPhone, but it's gotten a few updates since I first played it, and it just so happens to be free on May 10. It's an endless runner, but instead of a side-scroller, it runs from the top down, and it's got a few new elements to this genre. First, it's time-based, so not only do you need to run for as far as possible, but your goal is to hit the next checkpoint within a certain time limit.
Second, as your little dog runs along, you can "recruit" other dogs to run with you, which up your speed but also make it harder to maneuver around. Eventually, you hit a boundary (the cops catch your little dog that's been running amuck), and then you start over again from the beginning.
Off the Leash is great fun. The graphics are colorful and funny, the game's tilt-to-steer challenge is tough but not overwhelming at all, and especially at the low price, it's a great game to have on your iPhone. Definitely give it a download.